Effect of CeO₂ nanoparticles on the microstructure evolution and thermal reliability of pressureless sintered silver joints

Sintered silver (Ag) die-attach technology is widely used in high-temperature wide-bandgap semiconductor packaging due to its high melting point and robust mechanical properties. However, pressureless sintered Ag joints suffer from porosity evolution and crack propagation under cyclic thermo-mechanical loading. In this work, cerium oxide (CeO₂) nanoparticles (0–5 wt%) were introduced to regulate microstructural stability and fracture behavior. Microstructural characterization revealed that moderate CeO₂ addition (1–3 wt%) significantly increased joint densification and suppressed grain coarsening. Quantitative SEM analysis with image-based porosity mapping, sinter neck thickness measurement, and EDS elemental mapping revealed suppressed pore coalescence, stabilized neck morphology, and enhanced interfacial connection ratio in CeO₂-modified joints. The 1 wt% CeO₂-modified joints exhibited superior resistance to coarsening after 1000 h thermal aging at 250 °C. This stability is attributed to Zener pinning by the CeO₂ phase, which inhibited Ag grain growth and vacancy coalescence. Thermal shock testing (−60 °C to 150 °C) showed a fracture mode transition from edge delamination in pure Ag joints to distributed microcracking in CeO₂-modified joints, resulting in extended fatigue life. These results demonstrate that CeO₂ nanoparticle doping effectively enhances microstructural stability and thermomechanical reliability in pressureless sintered Ag interconnects.